The present invention relates generally to an apparatus for calibrating electric current sensors and, in particular, to a current sensor assembly.
Prior art analog based current sensors are designed to operate in a fixed range of current magnitudes. The lack of programmability means that multiple variations of current sensors need to be manufactured to accommodate applications requiring different current sensing ranges. Further, the prior art current sensors set the device gains/offsets by scribing resistive elements before final assembly or adjusting potentiometers. Both of these methods have drawbacks.
The present invention concerns an apparatus for calibrating sensors of electric current to ease problems brought on by part and process variations which affect sensor performance. The apparatus according to the present invention affords these sensors the flexibility to be calibrated to measure current levels in different working ranges appropriate for given applications. The innovative apparatus incorporates into the design of the sensor a Hall-effect magnetic field transducer element that enables the current measurement response function of the sensor to be programmed via the electrical interface connection of the sensor device. The primary parameters to be set via the connector interface are the transducer gain and offset.
The apparatus for sensing electrical current flowing in a conductor includes a toroidal core formed of a ferric material and having a slot extending through the core defining an air gap, the core having a central aperture, and an electrical current carrying conductor received in said central aperture, said core concentrating in said air gap magnetic flux generated by electrical current flowing in said conductor. A power supply is connected to the conductor for generating a known electrical current in the conductor and a Hall Effect sensor integrated circuit is positioned in the air gap and has a power supply pin and an output pin. A programming means is connected to the power supply pin and the output pin, whereby the integrated circuit responds to an application of a lower voltage first signal applied at the power supply pin by the programming means by generating at the output pin an output signal representing an amount of the known current flowing in the conductor and the integrated circuit responds to a higher voltage second signal applied at the power supply pin by accepting a programming signal applied at the output pin and calibrating the output signal in response to the programming signal.
The benefits of incorporating a sensing element programmable through the connector include: a) the ability to eliminate part-to-part variability and process variation of the end-of-line packaged units; and b) programmability allows the setting of both gain and offset after complete assembly thus permitting a single hardware implementation to meet the working electrical current ranges for different applications. The programmability enables the manufacturer to reduce the number of versions of parts needed to accommodate customer applications, thereby reducing costs.
Incorporation of the means to program the electric current sensor through the external electrical connector after final assembly bypasses the problems associated with the prior art current sensors in an economical and easily manufacturable way.
The current sensor assembly includes a housing having an annular portion for receiving the toroidal core. A tab is formed in the housing and extends into the core slot to align the core and prevent rotation of the core about its axis. The Hall Effect sensor integrated circuit is in the form of a chip that is positioned in the core slot adjacent to the tab. The tab and the chip are generally aligned in a plane extending radially from the axis of the annular portion of the housing. The tab has a thickness greater than a maximum thickness of the chip to function as a stop preventing the core from contacting the chip.